iOS Capture screen, then crop and mask the result image - iphone

Question

In my application, I want to do the following steps:
1 - Capture the screen, this part is no problem for me, I'm using the following code:
- (UIImage *)captureScreen {
UIGraphicsBeginImageContextWithOptions(self.view.frame.size, YES, 0.0f);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
2 - I cropped the image with this function
- (UIImage *)cropImage(UIImage *)image inRect:(CGRect)rect {
CGImageRef imageRef = CGImageCreateWithImageInRect(image.CGImage, rect);
UIImage *resultImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
return resultImage;
}
3 - Then I mask the cropped image with a pure black and white mask
- (UIImage *)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef maskedRef = CGImageCreateWithMask([image CGImage], mask);
UIImage *resultImage = [UIImage imageWithCGImage:maskedRef];
CGImageRelease(mask);
CGImageRelease(maskedRef);
return resultImage;
}
However, the result image I got is that outside the shape of the mask, the image is in black color instead of transparent. Can anybody help me?

Answer 1

This Works for me. Hope it will work for you too.
- (UIImage*) doImageMask:(UIImage *)mainImage:(UIImage*)maskImage{
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGImageRef maskImageRef = [maskImage CGImage];
// create a bitmap graphics context the size of the image
CGContextRef mainViewContentContext = CGBitmapContextCreate (NULL, maskImage.size.width, maskImage.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
if (mainViewContentContext == NULL){
return NULL;
}
CGFloat ratio = 0;
ratio = maskImage.size.width/ mainImage.size.width;
if(ratio * mainImage.size.height < maskImage.size.height) {
ratio = maskImage.size.height/ mainImage.size.height;
}
CGRect rect1 = {{0, 0}, {maskImage.size.width, maskImage.size.height}};
CGRect rect2 = {{-((mainImage.size.width*ratio)-maskImage.size.width)/2 , -((mainImage.size.height*ratio)-maskImage.size.height)/2}, {mainImage.size.width*ratio, mainImage.size.height*ratio}};
CGContextClipToMask(mainViewContentContext, rect1, maskImageRef);
CGContextDrawImage(mainViewContentContext, rect2, mainImage.CGImage);
// Create CGImageRef of the main view bitmap content, and then
// release that bitmap context
CGImageRef newImage = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
UIImage *theImage = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
// return the image
return theImage;
}

Answer 2

I solve my problem, it is due to the alpha channel of the image to be masked. So before masking, I create another UIImage with alpha channel and continue my steps.
This is the code for creating a UIImage with alpha
- (UIImage *)imageWithAlpha {
CGImageRef imageRef = self.CGImage;
CGFloat width = CGImageGetWidth(imageRef);
CGFloat height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(nil, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedFirst);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGImageRef resultImageRef = CGBitmapContextCreateImage(context);
UIImage *resultImage = [UIImage imageWithCGImage:resultImageRef scale:self.scale orientation:self.imageOrientation];
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
CGImageRelease(resultImageRef);
return resultImage;
}